The U.S. Immigration and Customs Enforcement (ICE) agency under former President Barack Obama may have failed to identify and arrest “highest risk” known or suspected terrorist aliens due to the absence of follow-up screenings after they are released.

Sanctuary cities that refused to cooperate with immigration authorities also prevented the agency from following up on the individuals in question, reveals a watchdog agency.

Based on a study of case files of detained aliens identified as known or suspected terrorists during fiscal years 2013 through 2015, the inspector general for the U.S. Department of Homeland Security (DHS) found:

ICE continues to face significant challenges with its screening of aliens who may have ties to terrorism. Auditors warn ICE may have missed opportunities to identify, apprehend, and adjudicate the status of aliens posing the highest risk to public safety and national security.